A series of catalysts consisting of small gold particles supported on cobalt oxide (Co3O4), were synthesized by co-precipitation and tested for their ability to oxidize dichloromethane (CH2Cl2). The addition of the small gold particles to the Co3O4 (which as the only catalyst has the highest activity for the oxidation of CH2Cl2 among the first row transition metal oxides) significantly improved the activity of the Co3O4. The rate constant at 300 degrees C was increased by a factor of 25. The activity was essentially independent of the gold loading at gold loadings between 0.2 and 10.0 wt.-%. In addition to this, the Au/Co3O4 catalysts were also significantly more active than noble metal catalysts, and exhibited activities 10 times higher than Cr2O3/Al2O3, 70 times higher than 0.5% Pt/Al2O3, and 560 times higher than 0.5% Pd/Al2O3 at 300 degrees C. The Au/Co3O4 catalysts selectively oxidized CH2Cl2 to CO2 and HCl (which can readily be stripped from air by a basic solution), and were quite stable at 350 degrees C in the presence of the oxidation products. In addition, water did not have an adverse effect on the catalytic activity. No detectable by-products (such as CHCl3 or CCl4) or partial oxidation products (CO, Cl-2, COCl2 and HCHO) were observed at 350 degrees C. The oxidation of CH2Cl2 was first order in CH2Cl2 concentration, with activation energies of ca. 20 kcal/mol.
